Re-download the installer.

If I remember correctly Apple let the cert expire on there installers and reissued just about everything they ever signed.

@jstillio It's a fresh installer I downloaded just over a week ago and it works fine when Airdropped to the target device just not when packaged and deployed via Composer and JAMF Pro.

I use this method without issue, and packaged one with Composer just last week.
- Download Install macOS Mojave.app via installinstallmacos.py
- Drag installer to Composer lefthand pane
- Create Applications folder in righthand pane
- Move Install macOS Mojave.app to newly created Applications folder, cleaning up folder structure that references where the installer was downloaded to.
- Click PKG button to create installer.
- Upload newly created .pkg to Jamf Admin
- Create policy to install newly created .pkg
- Run policy

Works every time as part of our Mojave startosinstall, eraseinstall workflow.
We use http distribution points and Jamf Pro 10.15.1

Thanks @merps will try that and report back.

If you have Xcode:

pkgbuild --install-location /Applications --component /Applications/Install macOS Catalina.app /private/tmp/Install_macOS_Catalina.app.pkg

I've taken a very different tack on this - I don't use Composer at all. Just drop the DMG downloaded via @gregneagle installinstallmacos.py into Jamf Admin, have a policy load that to / with a script run after to move it to /Applications and change the permissions (and clean up any other stuff like icons on root / ) and a Smart Group checking the presence of /Applications/Install macOS Mojave.app as scope for a policy to actually install it. It seems to work fairly reliably, and no need to worry about all the work of repackaging something that seems to be pretty sensitive.

I really wish there were a way to gather metrics across the JAMF estate - it would be very interesting to see the success rate vs time invested for the many possible solutions to deploying a major OS upgrade.